The present invention is related to Japanese patent application No. Hei. 11-180456, filed Jun. 25, 1999; No. Hei. 11-320188, filed Nov. 10, 1999; the contents of which are incorporated herein by reference.
The present invention relates to a refrigerating cycle apparatus, and more particularly, to a refrigerating cycle apparatus having a hot gas bypass function.
Generally, in vehicle air-conditioning systems, during winter heating, warm water (engine cooling water) is circulated through a heat exchanger for heating. Air-conditioning air is heated by this heat exchanger by using the warm water as a heat source. However, in this case, when the temperature of the warm water is low, the temperature of air blown into the passenger compartment of the vehicle is low, and the required heating effect is not obtained.
In an attempt to overcome this problem, Japanese Unexamined Patent Publication No. H.5-223357 proposes a refrigerating cycle apparatus capable of realizing a heating function by using hot gas bypass has been proposed. In this apparatus, when the warm water temperature is lower than a predetermined temperature, such as during engine starting, an auxiliary heating function is provided by feeding gas refrigerant delivered by a compressor (hot gas) into an evaporator. This approach bypasses the condenser, and heat from the gas refrigerant is transferred by the evaporator into the air-conditioning air. That is, the same heat exchanger mounted in an air-conditioning case, namely the evaporator, is used alternately to cool in a cooling mode and to heat during a heating mode.
Now, in the above described apparatus, during a heating mode, a high-side pressure is sensed at the discharge side of the compressor. When this pressure falls below a set value, the compressor is operated. However, when this pressure rises above the set value, compressor operation is stopped to prevent an abnormal rise in the high-side pressure.
While this apparatus has benefits, it provides no specific method for deciding the set value of the high-side pressure at which to stop compressor operation. However, experimental studies, carried out by the present inventors, show an operational problem with the compressor being stopped and restarted frequently during an extremely small period of time. More specifically, when in the hot gas bypass heating mode, the capacity of the high-pressure circuit part of the cycle is much lower than in the cooling mode. This is because high-pressure refrigerant from the compressor discharge side is fed directly to the evaporator, bypassing the condenser. Also, the hot gas bypass heating mode is used during cold temperatures when the outside air temperature is about xe2x88x9210xc2x0 C. Thus, there is much heat transfer from the high-pressure refrigerant to the low-temperature outside air. Consequently, when the operation of the compressor is stopped, the high-side pressure falls in an extremely short time to a value close to the low-side pressure.
As a result, the time period that the compressor operation stops and restarts is very short. And as a result, the life of an electromagnetic clutch controlling the compressor is shortened and the frequent stopping and restarting of the compressor (shock) reduces ride comfort. The present invention was developed in light of these drawbacks.
It is therefore an object of the present invention to control heating capacity obtained by hot gas bypass system without giving rise to frequent stopping and restarting of a compressor.
It is another object of the present invention to control heating capacity obtained by hot gas bypass system without stopping and restarting of a compressor causing switching of refrigerant conduits.
Accordingly, the objects of the present invention are accomplished by providing a refrigerating cycle apparatus capable of being operated in a hot gas bypass heating mode, wherein by the discharge side of a compressor is directly connected through a hot gas bypass conduit to the inlet side of an evaporator (18). The evaporator acts as a radiator heated by gas refrigerant. The invention comprises a stop control means (S180, S200) which stops the compressor when, during a heating mode, the high-side pressure at the compressor discharge side rises above a set value. An operation restart control means is provided for restarting the compressor when, while the compressor is stopped, a heating capacity falls below a set value which indicates that there is no heating capacity.
When the compressor is temporarily stopped, It is maintained in an off condition until the heating capacity falls below a set value indicating that there is no heating capacity. Consequently, the compressor is not restarted within a short time, it is possible to prevent problems such as decreasing the life of an electromagnetic clutch by frequent stopping and restarting.
Furthermore, after the compressor is stopped, there is a temperature difference between the temperature of the evaporator surface and the air passing over it. This difference is due to the heat capacity of the evaporator and remains until the heating capacity falls below a set value indicating that there is no heating capacity. However, in the present invention, the compressor can be restarted while this temperature difference remains. Therefore, the heating capacity does not fall too far due to the compressor being stopped for a long period of time. Thus, in the on/off-control of the compressor, the heating capacity is accurately controlled while problems, such as shortened life of the electromagnetic clutch, are prevented.
In another aspect of the present invention, a refrigerating cycle apparatus having a hot gas bypass conduit directly connecting the discharge side of a compressor to the inlet side of an evaporator is provided. The apparatus has a valve means for switching the connection between the discharge side of the compressor and the hot gas bypass conduit. The apparatus also has a connection between the discharge side of the compressor and a condenser and is capable of operating in a hot gas bypass heating mode.
The discharge side of the compressor is directly connected through the valve means and the hot gas bypass conduit to the inlet side of the evaporator. As such, the evaporator is made to act as a radiator, which is heated by gas refrigerant. The apparatus generally comprises a first control means for controlling the valve means that refrigerant flows to the condenser side when, in the heating mode, a high-side pressure at the compressor discharge side rises above a set value. A second control means for restoring the valve means to a heating mode operation state thereof when a heating capacity in the evaporator falls below a set value which indicates there is no heating capacity.
As such, the heating capacity, obtained during hot gas bypass by refrigerant flow control using the valve means, can be accurately controlled. Thus, heating capacity control can be carried out by switching of refrigerant conduits without stopping and restarting the compressor, and fluctuations of compressor torque can be suppressed.
As provided in another aspect of the present invention, the first control means controls the valve means so that the connection between the discharge side of the compressor and the hot gas bypass conduit and the connection between the discharge side of the compressor and the condenser are both open. By this means, it is possible to carry out heating capacity control with refrigerant flowing to the hot gas bypass conduit side and to the condenser side in parallel.
In another aspect of the present invention, the first control means controls the valve means to close the connection between the discharge side of the compressor and the hot gas bypass conduit and open the connection between the discharge side of the compressor and the condenser. As a result, heating capacity control is carried out with the same state as during the cooling mode of the apparatus. In another aspect of the invention, at least one or the other of the set values pertaining to the high-side pressure and the heating capacity are corrected based on heat load. As a result, in on/off-control of the compressor, because the compressor operating time is corrected according, to heat load, on/off-control of the compressor can be controlled appropriately corresponding to heat load.
In another aspect of the present invention, a quantity relating to heat load is an outside air temperature or the temperature of a room being heated. As provided in a further aspect of the present invention, an apparatus having a warm water type heat exchanger for heating is provided. This device constitutes the main heating device and is disposed on the air downstream side of the evaporator. A quantity representing the heating load is the temperature of warm water circulating through the heat exchanger or the outlet temperature of air blown into a room through an outlet downstream of the heat exchanger.
As set forth in a further aspect of the present invention, a quantity representing the heating capacity is the refrigerant pressure in the cycle during compressor stoppage. Here, either the high-side pressure or the low-side pressure can be used as the refrigerant pressure in the cycle.
In another aspect of the present invention, the quantity representing the heating capacity is the refrigerant pressure in the cycle during a compressor stoppage. When as a result of the stoppage of the compressor the refrigerant pressure falls to the vicinity of a saturation pressure with respect to the outside air temperature the compressor is restarted.
When the compressor is stopped, high side pressure falls more rapidly and the rate of heat transfer from the high-pressure refrigerant to the outside air increases as the outside air temperature drops. However, because the saturation pressure of the outside air temperature also falls with outside air temperature, in this aspect of the present invention, the refrigerant pressure at which the compressor is restarted becomes low when the outside air temperature is low. As a result, because the refrigerant pressure at which the compressor is restarted becomes low and the high-side pressure falls more rapidly, these conditions may cancel each other out. Therefore, the time that compressor is stopped is prevented from becoming short when the outside air temperature is low. Therefore, the time that compressor is stopped is kept substantially constant, irrespective of changes in the outside air temperature.
In another aspect of the present invention, the quantity representing the heating capacity is the temperature of evaporator. As set forth in an eleventh aspect of the present invention, the quantity representing the heating capacity is the temperature of evaporator. Also, the compressor is restarted when the temperature of the evaporator has fallen to a temperature of about the outside air temperature due to stopping operation of compressor.
In another aspect of the present invention, a refrigerating cycle apparatus capable of being operated in a hot gas bypass heating mode, wherein by the discharge side of a compressor is directly connected through a hot gas bypass conduit to the inlet side of an evaporator. The evaporator acts as a radiator heated by gas refrigerant. The invention comprises a stop control means which stops the compressor when, during a heating mode, the high-side pressure at the compressor discharge side rises above a set value. An operation restart control means for restarting the compressor when the time for which the compressor has been stopped reaches a set value.
As a result, the compressor is restarted after it has been forcibly stopped for a set time pertaining to the operation restart control means. As such, the time which the compressor is stopped can easily be kept constant irrespective of changes in usage conditions.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within he spirit and scope of the invention will become apparent to hose skilled in the art from this detailed description.